Drill resistant hard plate and method for manufacture thereof

Abstract

A highly drill-resistant element, suitable for inclusion into the walls and/or doors of a security container to resist drilling to access the contents of the container is formed by welding onto a steel plate formed of REPUBLIC 100-AR (TM) steel a layer of Tube BORIUM® material by a known tungsten-inert-gas (TIG welding process). The REPUBLIC 100-AR (TM) steel has a chemical composition and is manufactured to inherently possess a very high yield strength and abrasion resistance. The Tube BORIUM® material, welded by the thick process, provides a very hard and drill-resistant layer comprising a heterogenous suspension of tungsten carbide particles of selected size in a steel matrix.

What is claimed is: 
     
       1. A process for manufacturing a hard drill-resistant element, comprising the step of: (a) providing a filler material comprising a steel tube having 5-40 mesh tungsten carbide particles therein;   (b) providing a steel plate; and   (c) forming a layer of said tungsten carbide particles suspended in a steel matrix on said steel plate by welding said filler material using tungsten inert gas welding conditions, said layer having a compositional gradient of tungsten carbide particles from an outer surface of said layer to said steel plate, such that said tungsten carbide particles are concentrated in said layer at a location removed from said outer surface to provide said drill resistance.   
     
     
       2. The process according to claim 1, comprising the further step of: placing the welded element in sand after the welding step for a minimum of one hour of slow cooling to prevent formation of cracks more than about 0.01 in. wide or warpage more than about 0.06 in. per side as measured with the element in an unloaded state with said welded-on layer uppermost.   
     
     
       3. The process according to claim 2, comprising the further step of: grit-blasting an exposed surface of said welded-on layer to remove scale therefrom.   
     
     
       4. The process according to claim 3, wherein: said grit-blasting comprises impinging aluminum oxide particles to said exposed surface.   
     
     
       5. The process of claim 1 wherein said tungsten carbide particles range between about 10 and 20 mesh. 
     
     
       6. A drill-resistant hard plate for a security container, comprising: a steel plate having a weld-receiving surface; and a drill-resistant layer comprising tungsten carbide particles ranging from 5 to 40 mesh suspended in a steel matrix, welded to said weld-receiving surface by tungsten-inert-gas welding, said layer having a compositional gradient of tungsten carbide particles from an outer surface of said layer to said steel plate, such that said tungsten carbide particles are concentrated in said layer at a location removed from said outer surface to provide said drill resistance, said welding forming said drill resistant plate with a generally flat upper surface, wherein said tungsten-inert-gas welding further comprises the steps of providing a filler material comprising a steel tube having 5-40 mesh tungsten carbide particles therein and forming said drill resistant layer on said steel plate by welding said filler material using tungsten-inert-gas welding conditions.   
     
     
       7. Drill-resistant hard plate according to claim 6, wherein: said steel plate has a through hole formed therein, and said drill-resistant layer is formed to surround said through hole without extending therein.   
     
     
       8. The drill-resistant plate of claim 6 wherein said tungsten carbide particles range between about 10 and 20 mesh. 
     
     
       9. A drill-resistant hard plate element for a security container, comprising: a steel plate having a weld-receiving surface; and a drill-resistant layer comprising tungsten carbide particles ranging from 5 to 40 mesh suspended in a steel matrix, welded to said weld-receiving surface by tungsten-inert-gas welding, said layer having a compositional gradient of tungsten carbide particles from an outer surface of said layer to said steel plate, such that said tungsten carbide particles are concentrated in said layer at a location removed from said outer surface to provide said drill resistance said welding forming said drill resisted plate with a generally flat upper surface,   wherein, upon completion of said tungsten-inert-gas welding, the plate is further processed by placing the plate in sand for a minimum of one hour of slow cooling to prevent formation of cracks more than about 0.01 in. wide or warpage of more than about 0.06 in. per side, as measured with the plate in a unloaded state with said welded-on layer uppermost.